1. Field of the Invention
The present invention relates to casterwheel structures and more particularly to casterwheel structures which permit vertical adjustment of the level of the implement above the terrain and which also permit vertical movement of the casterwheel.
2. Discussion of the Prior Art
Modern farming implements such as rotary mowers, rotary cutters and shredders typically have casterwheels mounted on the rear thereof. In some applications it is desirable to have a casterwheel assembly in which the height of the implement is variable. One method of changing the height of the implement is to provide a casterwheel assembly which can be disassembled and remounted at any of several incremental positions. While such a construction provides some variability, often incremental adjustments do not permit desired positioning of the implement and are disadvantageous from the standpoint of the time and effort expended in readjustment. Furthermore, such construction does not protect the implement from shock received from rough terrain.
The desirability of providing continuous adjustment has been recognized and various solutions proposed, including the use of a hydraulic cylinder and piston as shown in U.S. Pat. No. 2,502,309 issued to Byrd or the use of a two part threaded casing which houses a spring, the tension on which can be changed by rotating one part of the casing relative to the other to compress or relieve force on the spring as shown in U.S. Pat. No. 3,664,433 issued to Bo.
The art has also taught the use of pantographic linkages to achieve vertical movement of the implement relative to the casterwheel. U.S. Pat. Nos. 1,968,046 to Linn and 2,312,553 to Hudson, for example, disclose such structures. Hudson and Linn permit vertical movement of the casterwheel and teach that the casterwheel can be biased to a neutral position by shock absorbing means. However, the pantographic linkage used by Hudson and Linn does not permit continuous adjustment of the implement above the terrain.